1. Field of Invention
This invention pertains to the field of telecommunications, and particularly to telecommunications involving mobile stations operating in context of a cellular mobile telecommunications system.
2. Related Art and Other Considerations
In mobile telecommunications, mobile stations such as mobile telephones communicate over radio channels with base stations. Typically a plurality of base stations are, in turn, connected to a mobile switching center. The mobile switching center is usually connected, e.g., via a gateway, to other telecommunication networks, such as the public switched telephone network.
Traditionally the radio transmissions of each base station cover a geographical area, e.g., one or more "cells". A predetermined number of cells typically form a location area. When an active mobile station travels from an old cell to a new cell, a handoff or handover must occur from the base station handling the old cell to the base station handling the new cell. A mobile station in an idle mode can move or "roam" from an old cell to a new cell, and even change location areas.
In a telecommunications network, certain information concerning a mobile station is stored in a home location register (HLR). As the mobile station travels into a location area that is handled by a different mobile switching center, a location update operation must occur so that both the home location register (HLR) and a visitor location register (VLR), typically at the mobile switching center, have appropriate current information about the mobile station and its whereabouts. In this regard, when a mobile station travels into an area having a different location identifier, a forced registration typically occurs. In the forced registration, the home location register (HLR) is updated regarding the particular mobile switching center now serving the mobile station.
When a call is placed to a mobile station, the cellular network "pages" the mobile station in certain cells, e.g., location area, based on stored information indicative, e.g., of where the mobile station has roamed or is currently located. The paging signals are sent from the mobile switching center to concerned base stations which handle the certain cells.
Operators of mobile telecommunications systems, e.g., telecommunications providers or telecommunications companies, typically have subscription agreements to the mobile subscribers. Generally the subscription agreements assess differing fees or tariffs depending on such circumstances as number of calls, time of call, distance covered by call (e.g., long distance), etc.
Operators of cellular-based telecommunications networks have an opportunity to increase revenue when subscribers are encouraged to increase utilization of the mobile stations. To this end, in areas with low traffic density there may be spare capacity that could be offered to subscribers. The spare capacity can be offered to subscribers at a lower tariff but subject to restrictions which are not applicable to regular tariff calls. One example of such a restriction is a geographical restriction, i.e., restricting the mobile subscriber to use the mobile station only in specified cells.
EP 641137 discloses a memory card (e.g., SIM) situated within a mobile station, the SIM card having a stored local area identification. Access to a network is only permitted when the stored local area identification agrees with a broadcast local area identifier, thereby restricting the user's access to the mobile network to a defined local area. Provision therefore must be made at the mobile station for permission to complete a call or allow a call to originate from the mobile station, thereby increasing the complexity of the mobile station. Moreover, changing the restricting local area identification necessities preparation and delivery of a new SIM card. Further, SIM cards are not universally available.
What is needed therefore, and an object of the present invention, is a flexible and convenient technique for geographically restricting operation of a mobile station in a cellular telecommunications network.